Increasingly smaller electronic components such as semiconductor chips have been required recently, and for example, thinner semiconductor chips are produced. Warpage occurs in electronic components upon boding electronic components, or electronic components and substrates, with an adhesive. This has become an important issue. Semiconductor chips are mounted on a substrate by reflow soldering (heating the entire substrate with infrared rays and the like), and a package is heated to a high temperature of 200° C. or higher. Then, moisture contained in the package, especially in an adhesive layer rapidly evaporates and expands to cause package cracks and reduction in reliability of a semiconductor device. Accordingly, there is a demand for solving the problem of reflow cracks at high levels.
In order to prevent warpage, an adhesive for electronic components is generally designed so that a cured product thereof has a low elastic modulus. However, reflow crack resistance tends to be deteriorated in the case of using an adhesive for electronic components, whose cured product has a low elastic modulus. Warpage and reflow cracks are less likely to be simultaneously prevented.
Patent Document 1 proposes a resin paste containing a specific imide compound, a liquid rubber compound such as epoxidized polybutadiene, a radical initiator, and a filler in order to prevent warpage and reflow cracks. Patent Document 1 suggests that, since a cured product of such a resin paste has a low stress, warpage and reflow cracks can be prevented. However, in the case that a thin semiconductor chip having a thickness of about tens of micrometers is bonded to a substrate with the resin paste described in Patent Document 1, problematically, the elastic modulus of the cured resin is high and a chip has a large warpage.
Patent Document 2 discloses an epoxy resin composition containing an epoxy resin and an episulfide resin, as an epoxy resin composition with improved reflow crack resistance particularly to copper. Patent Document 2 discloses that bisphenol A episulfide resin is preferable as the episulfide resin, and bisphenol epoxy resin is preferable as the epoxy resin. However, also upon using the epoxy resin composition described in Patent Document 2, problematically, the elastic modulus of a cured resin is high and a semiconductor chip having a thickness of about tens of micrometers has a large warpage.